Pump



June 4, 1963 A. BENTZINGER PUMP Filed Dec. 21. 1960 United States Patent 3,092,032 PUMP Harlan A. Bentzinger, Wayland, Mass, assignor to Precision Chemical Pump Corporation, Waltham, Mass, a corporation of Massachusetts Filed Dec. 21, 1960, Ser. No. 77,424 2 Claims. (Cl. 103-150) This invention relates to pumps and more particularly to a novel positive displacement sealed piston pump especially useful for the accurate pumping of liquids, solutions, and the like at high pressures of upwards of 250-500 p.s.i.

Sealed pumps of the diaphragm type with the customary check valves have long been used for supplying a stream of liquid, especially a corrosive liquid, at a predetermined rate because of their simplicity and reliability as well as because their construction enabled the ready use of nonmetalli-c unreactive materials such as rubber and plastics as their pumping elements. However, such pumps have not generally been useful at pressures much in excess of 100 psi. because of the bending and eventual failure of the diaphragm or portion thereof; even at lower pressures the pumping accuracy was not as great as desired especially under conditions of varying pressure. Also, the tensioning of the diaphragm by flexing it, this being most pronounced adjacent the line of support of its outer edge, eventually caused failure of the diaphragm in that region, and this happened much more rapidly at higher pressures.

Accordingly, it is a major object of the present invention to provide a novel positive displacement sealed piston pump accurate to within 1% under the usual pumping conditions, in spite of varying pressures and wherein the degree of failure is reduced to a surprising extent. This has been accomplished by providing, instead of the usual diaphragm having a relatively thin flexible portion for permitting the necessary pumping movement, a novel sealed piston having rigid inner and outer portions connected by a relatively radially narrow but axially wide annular band of an elastomeric material having the characteristics of an incompressible fluid, with such material being adhesively bonded to the closely spaced generally parallel opposing surfaces of the inner and outer rigid portions, rather than simply being clamped in position. By utilizing such novel structure, the elastomeric material, rather than being subjected to bending and tension :forces during pumping operation, is stressed primarily in shear, and this, in [addition to enabling the construction of a structure able to resist high pressures, has the unexpected result of providing greatly improved diaphragm life especially when subject to chemical attack and aging. Furthermore, the use of but a narrow band of deformable material, with the major portion of the structure being rigid, provides but a minute volumetric distortion upon pressure changes and so results in better pumping accuracy.

For the purpose of more fully explaining the above and further objects and features of the invention, reference is now made to the following detailed description of preferred embodiments of the invention, together with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional elevation of a preferred embodiment of the pump of the invention;

FIG. 2 is a cross-sectional plan of the pump of FIG. 1; and

FIGS. 3-5 are partial cross-sections showing in simplified embodiment the operation of a pump of the invention.

A pump unit of the type herein shown may comprise a small electric motor, a reciprocable rod for operating the diaphragm, and operative connections between the rod and the motor usually including a train of reduction gearing. This mechanism is usually mounted in a closed oil filled body through a wall of which the reciprocable rod projects. The pumping chamber, one wall of which is formed by the movable diaphragm, is provided with the usual inlet and outlet openings having conventional check valves associated therewith for control of the movement of fluid in the desired direction as the pump operates. If desired, the other wall of the pumping chamber may be of transparent material to permit inspection while the pump is operating. These aspects of the present structure are well known in the art and so require no further explanation except as [to their association with the present invention.

Referring to the drawings, the pump body is shown at 12 and the reciprocable rod at 14, both being broken away so as to show only their connection to the pump head with which the present invention is concemed. The pump body 12 at its end portion as shown has the form of a ring with an annular seating surface 16 perpendicular to the ring axis. The rod 14 lies along the ring axis and has a threaded end portion 15.

In accordance with the principles of the present invention a pumping member is provided attached to the annular body seating surface 16 and to the rod 15. Such member in essence comprises a rigid annular outer mem ber 22 positioned against seating surface 16, a rigid central member 25 positioned within the outer member and an elastomeric material 28 having the characteristics of an incompressible fluid interposed by adhesive bonding between the outer cylindrical surface 26 of said central member and the opposed parallel inner cylindrical surface 23 of the outer annular member 22. The circular opening of the outer annular member 22 may be considered to define the total diaphragm area, with the elastomeric material 28 forming a narrow band within it such that the diameter of the rigid central member 25 is a large proportion of the diameter of said opening. It is also important that the elastorneric material be relatively thick in an axial direction in proportion to its width in a radial direction so that it will be stressed mainly in shear, a ratio of at least about 2:1 as shown in FIGS. 3-5 being preferable for pressures of 250 psi. or even more being desirable as pumping pressures are increased. For example, at pressures of about 500 p.s.i., a ratio of 4:1 as shown in FIG. 1 is preferred, while at higher pressures higher ratios are required in about the same proportions. The elastomeric material must be bonded between the opposed parallel concentric surfaces 23, 26 of the inner and outer members 22, 25 to provide a uniform cross section throughout its annular ring. Preferably, the elastomeric material is also bonded to the working face of the central member 25 and of the annular member 22 throughout their entire extent as at 27 mainly to aid in protecting the metallic rigid elements from chemical attack by liquids passing through the pump. Additionally, the elastorneric working face 27 is provided with an annular ridge 29 adjacent the inner edge of the outer member 22 to provide a substantial degree of preloading the elastomeric material 28 in compression in the direction of application of fiuid pressure, as shown by the arrow thereat in FIG. 1. Ridge 29 also functions as a seal. A plurality of holes 21 is provided in the outer member 22 and its working face '27 for attachment to body 12 as hereinafter set forth.

Outwardly of the pumping member of the invention as described above is provided a pump housing 30. Said pump housing has a central recess 31 producing with the pumping member a pumping chamber of a diameter generally the same as the inner diameter of the annular member 22. Suitable inlet and outlet openings 32 are provided into said chamber. If desired, housing 30 may be of transparent plastic or the like. The housing is also provided with a plurality of holes 34 matching those of the annular member 22 and suitable threaded holes in body 12 for receiving bolts 36 to clamp the assembly together.

The operation of the structure is conventional from a pumping standpoint but insofar as the present invention is concerned may best be seen by reference to FIGS. 3-5 wherein is shown a simplified embodiment omitting a working face covering of elastomer. Thus, the advanced piston position is shown in FIG. 3, the midposition in FIG. 4, and the retracted position in PK]. 5. FJG. 1 shows the midposition with the prccompression shown by the small arrows under ridge 29. This latter is a useful feature in preventing bond separation at higher pressures, since the shear stress of operation (NUS. 3 and 5) will tend to separate the surfaces along the bonded surfaces 23, 36.

The selection of a suitable elastomeric material must be made with care especially as to its deformation and bonding characteristics, as well as to its resistance to chemical attack. Such materials as natural rubber, butyl rubber, buna N, Hypalon, a chloro-sulfonated polyethylene and Viton. a copolymer of hcxafluoropropylene and vinylidene fluoride, made by Du Pont, are typical examples of satisfactory elasto-mcrs. As for its deformation, it has been found that relatively high deformation forces are necessary to resist the high pressures for which the pump of the invention is particularly useful. Thus with a piston area of about 3 square inches, and hence a periphery of about 3 linear inches capable of resisting at least 250 p.s.i., the total shear will be about 160 pounds per linear inch across the ring which must be resisted by the bonding, such force producing a deflection of about 0.05 inch forward and back from a neutral position. Minimum bond strength should preferably be at least double the deflection force at a desired deflection and preferably even higher. In general, with a pump capable of resisting a force of F p.s.i., with an area A and a ring of L inches periphery, the minimum bond strength per linear inch will be defined as FA/L which must be greater than about 100 and preferably at least twice that value. Bond strengths, in brief, must be adequately high to resist both the static fluid pressure and the pumping deformation which may be calculated for a given high pressure pump.

Bonding of elastomeric materials such as rubbers and plastics to rigid materials such as metals, rigid plastics, etc. to provide such shear strengths is well known in the art and hence need not herein be discussed in detail.

Thus, it will be seen that the invention provides a novel sealed piston pump having high pressure and other characteristics not heretofore available in such pumps. Various modifications of the invention within the spirit there-of and the scope of the appended claims will be apparent to those skilled in the art.

I claim:

1. A pump head for a high pressure pump comprising a pump body with an annular seating surface therearound, a piston pumping member having a rigid annular outer member positioned against said seating surface and a central opening therewithin, a reciprocable pump rod, a rigid central member connected to and reciprocable by said pump rod positioned within the central opening of said annular member and an elastomeric material having the characteristics of an incompressible fluid interposed between an outer cylindrical surface of said central member and an opposed parallel concentric inner surface of said annular member with an axial dimension substantially greater by about the ratio of 2:1 than the distance between said opposed surfaces and adhesively bonded to said opposed surfaces to stress said material primarily in shear during axial movement of said central member relatively to said annular member and a pump housing providing with said pumping member a pump chamber, and fastening means effective to clamp said pumping member at its annular member between said housing and said annular seating surface of said pump body.

2. A pump head for a high pressure pump comprising a pump body with an annular seating surface therearound, a piston pumping member having a rigid annular outer member positioned against said seating surface and a central opening therewithin, a reciprocable pump rod, a rigid central member connected to and reciprocable by said pump rod positioned within the central opening of said annular member and an elastomeric material having the characteristics of an incompressible fluid interposed between an outer cylindrical surface of said central member and an opposed parallel concentric inner surface of said annular member with an axial dimension substantially greater by about the ratio of 2:1 than the distance between said opposed surfaces and extending throughout the surfaces of said annular member and said central member, a housing positioned outwardly of said pumping member, a raised annular ridge formed on said elastomerie material and between said housing and said an nular member, said material adhesively bonded at a bond strength FA/L of at least a value of about pounds per linear inch to said opposed surfaces to stress said material primarily in shear during minimum axial movement of said central member relatively to said annular member and said housing providing with said pumping member a pump chamber, and fastening means effective to clamp said pumping member at its annular member between said housing and said annular seating surface of said pump body.

References Cited in the file of this patent UNITED STATES PATENTS 2,712,793 Holm July 12, 1955 2,741,187 Moller Apr. 10. 1956 FOREIGN PATENTS 2,368,132 France Jan. 30, 1945 

1. A PUMP HEAD FOR A HIGH PRESSURE PUMP COMPRISING A PUMP BODY WITH AN ANNULAR SEATING SURFACE THEREAROUND, A PISTON PUMPING MEMBER HAVING A RIGID ANNULAR OUTER MEMBER POSITIONED AGAINST SAID SEATING SURFACE AND A CENTRAL OPENING THEREWITHIN, A RECIPROCABLE PUMP ROD, A RIGID CENTRAL MEMBER CONNECTED TO AND RECIPROCABLE BY SAID PUMP ROD POSITIONED WITHIN THE CENTRAL OPENING OF SAID ANNULAR MEMBER AND AN ELASTOMERIC MATERIAL HAVING THE CHARACTERISTICS OF AN INCOMPRESSIBLE FLUID INTERPOSED BETWEEN AN OUTER CYLINDRICAL SURFACE OF SAID CENTRAL MEMBER AND AN OPPOSED PARALLEL CONCENTRIC INNER SURFACE OF SAID ANNULAR MEMBER WITH AN AXIAL DIMENSION SUBSTANTIALLY GREATER BY ABOUT THE RATIO OF 2.1 THAN THE 